Once I thought if it is possible to get different circles together. I tried and the consequences were disastrous. The reason was plainly described by her. Actually, we live different lives in different friend circles. My behaviour and status in my college group would be entirely different from that in high school. An event where friends from different circles come together would lead to ambivalence and hence discomfort.
For most of the people, friends are more important than anything. I believe the reason is the equal platform on which a friend exist, which is not possible for a father or brother. The circle of trust is more firmly created when you share a secret with an equivalent. Again, different friend circles contain a separate set of secrets and emotions. It is wise to keep them separate.